When you think that there is a mistake in an RFC, it is wise to check the RFC errata list at http://www.rfc-editor.org/errata_list.php
In the list, you will see that Dr. Mills reported this typo back in 2001. Terje Mathisen wrote: > Lei wrote: >> In RFC 2030(written by Prof. D.Mills), we have roundtrip delay time >> formula as follows: >> >> d = (T4 - T1) - (T2 - T3) .................(1) >> >> However, IMHO, it should be >> >> d = (T4-T1) - (T3 - T2)....................(1)' > > This is the same as > > d = -T1 + T2 -T3 +T4 > or > d = (T2-T1) - (T3-T4) > > right? > > "Use the source, Luke" :-) > > From ntp_proto.c, around line 1200: >> * Let t1 = p_org, t2 = p_rec, t3 = p_xmt, t4 = peer->rec: >> */ >> ci = p_xmt; /* t3 - t4 */ >> L_SUB(&ci, &peer->rec); >> LFPTOD(&ci, t34); >> ci = p_rec; /* t2 - t1 */ >> L_SUB(&ci, &p_org); >> LFPTOD(&ci, t21); > > I.e Dr. Mills have here calculated (T3-T4) and (T2-T1), both of which > should be small (normally positive) numbers, and the difference between > them is the same as in your formula. > > The conclusion is that I'm almost certain you've found a typo in the RFC: > > The total on-network-cable time must of course be the total time from > request to reply (T4-T1), minus the time spent inside the server > (T3-T2), so your second version is correct. > > Assuming the RFC does indeed use the first form, that would also be > against the written description of the algorithm. > > Terje > _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
